Web Database Applications with PHP, and MySQL

Functions

Functions and operators can be used in SQL statements. This section lists these functions and operators and provides examples. A full list of functions with examples is available in Section 7.4 of the manual.html file distributed with MySQL.

Arithmetic and comparison operators

Table 3-2 shows examples of the basic arithmetic and comparison operators in SELECT statements. The basic arithmetic operators are *, +, /, and -, as well as the parentheses ( ) to control the order of evaluation of an expression.

Table 3-2. Using the arithmetic and comparison operators

Statement	Output
SELECT 8+3*2;	14
SELECT (8+3)*2;	22
SELECT 2=2;	1
SELECT 1!=2;	1
SELECT 2<=2;	1
SELECT 3<=2;	0

The comparison operators include =, !=, <, >, <=, and >=. Four examples are shown in Table 3-2. If an expression evaluates as true, the output is 1; if an expression evaluates as false, the output is 0. To test for equality, a single equals sign is used; this contrasts with PHP, where the double equals (==) is used for equality tests, and a single equals sign is used for assignment.

To test whether two items are equal, the != operator is provided. Less-than-or-equal-to is represented by <=, and greater-than-or-equal-to is represented by >=. Parentheses can explicitly express the evaluation order.

String-comparison operators and functions

Table 3-3 shows examples of the MySQL string-comparison operators and functions. Many of the MySQL string functions shown here are similar to PHP functions, ...